Decreased locomotor activity in mice expressing tTA under control of the CaMKIIα promoter

Transgenic mice in which the tetracycline transactivator (tTA) is driven by the forebrain-specific calcium-calmodulin-dependent kinase II alpha promoter (CaMKII alpha-tTA mice) are used to study the molecular genetics of many behaviors. These mice can be crossed with other transgenic mice carrying a transgene of interest coupled to the tetracycline-responsive promoter element to produce mice with forebrain-specific expression of the transgene under investigation. The value of using CaMKII alpha-tTA mice to study behavior, however, is dependent on the CaMKII alpha-tTA mice themselves lacking a behavioral phenotype with respect to the behaviors being studied. Here we present data that suggest CaMKII alpha-tTA mice have a behavioral phenotype distinct from that of their wild-type (WT) littermates. Most strikingly, we find that CaMKII alpha-tTA mice, both those with a C57BL/6NTac genetic background (B6-tTA) and those with a 129S6B6F1/Tac hybrid genetic background (F1-tTA), exhibit decreased locomotor activity compared with WT littermates that could be misinterpreted as altered anxiety-like behavior. Despite this impairment, neither B6-tTA nor F1-tTA mice perform differently than their WT littermates in two commonly used learning and memory paradigms - Pavlovian fear conditioning and Morris water maze. Additionally, we find data regarding motor coordination and balance to be mixed: B6-tTA mice, but not F1-tTA mice, exhibit impaired performance on the accelerating rotarod and both perform as well as their WT littermates on the balance beam.